1. Field of the Invention
The present invention relates to processes for producing a salt of N-guanidino thiourea and 3-amino-5-mercapto-1,2,4-triazole, which are useful as intermediate materials for medicines and pesticides. More specifically, it relates to a process for a salt of N-guanidino thiourea (i.e., "GTU salt"), which is an intermediate for 3-amino-5-mercapto-1,2,4-triazole (i.e., "ASTA"), by reacting, while heating, (i) a compound having both a thiocyanate group and an aminoguanidino group, or (ii) (a) a compound having a thiocyanate group and (b) a compound having an aminoguanidino group, in the presence of an acid, while heating, in a polar solvent. Furthermore, the resultant GTU salt can be converted to ASTA by heating the same under alkaline conditions.
2. Description of the Related Art
Several processes for producing ASTA are already known in the art. For example, DE-A-1960981 proposes a process for producing ASTA by dissolving aminoguanidine bicarbonate in ethanol containing acetic acid dissolved therein, followed by charging gaseous carbon disulfide thereto, after adding triethylamine, as follows. ##STR1##
However, this process has the problems that the carbon disulfide reagent is toxic, flammable and explosive, and therefore, the production plant becomes expensive because special precautions must be taken in the apparatus (for example, the use of closed or sealed apparatus and the installation of means for treatment of exhaust gases and waste water, etc.).
U.S.S.R. Patent No. 1002291 proposes the synthesis of ASTA by reacting aminoguanidine hydrochloride and thiourea in a molten state in the absence of a solvent as follows. ##STR2##
However, this process also has the problems that the reaction yield is not satisfactory. In addition, the starting thiourea is said to be toxic and carcinogenic, and therefore, the production plant becomes expensive.
Further, JP-A-59-124333 discloses a process for producing ASTA by reacting, while heating, GTU hydrochloric salt by dissolving the same in an aqueous sodium hydroxide. However, this publication does not disclose a method for preparing GTU. Furthermore, the present inventors proposed in JP-A-5-247004 the preparation of ASTA is prepared by reacting, in the absence of a solvent, aminoguanidine thiocyanate, or a salt of aminoguanidine and a salt of thiocyanic acid. However, this process still has the problems that the reaction rate and yield are not commercially satisfactory.